A series of web attacks by spammers have forced a security firm to end an initiative to curb junk mail.
The company has explained why its anti-spam effort is ending
Israeli start-up Blue Security used a variety of tactics to make spammers clean up the lists of addresses to which they sent junk mail.
The firm also automatically filled in forms on spammers' websites to get names taken off the mailing lists.
But escalating attacks from spammers annoyed by the initiative's success has led to its closure.
Blue Security set up the Blue Frog anti-spam scheme in July 2005 and since then has signed up more than 500,000 members.
The scheme involved users reporting to Blue Security every spam message they received. The security firm would then contact the spammers who sent the mail and ask them to remove the name of that user from their mailing list.
If this method of stopping spam failed, Blue Security would then visit the spammer's websites advertising the products seen in junk mail and fill in any forms asking for users' names be removed from the list.
This could mean that some spammers' websites were getting thousands of requests for mailing lists to be cleaned up every day.
Blue Security claimed that the scheme reduced spam for many of those that signed up.
The tactic of bombarding spammers' websites was controversial among many anti-spam workers.
Sense of responsibility
The first indication that some junk mailers had taken exception to the anti-spam efforts came in early May when Blue Security was hit by a large so-called Distributed Denial of Service attack.
In such attacks websites get bombarded with huge amounts of data that their servers cannot handle.
At the same time some of those that had signed up for Blue Security's anti-spam system started getting threatening messages.
Blue Security realised that if it re-started its anti-spam campaign the attacks would get worse as the spammers seemed to have a huge network of remotely-controlled computers under their control.
"We cannot take the responsibility for an ever-escalating cyber war through our continued operations," said a statement on Blue Security's website.
As a result the company has decided to discontinue its anti-spam efforts.
"We believe this is the responsible thing to do," said the statement.
The company said it would now explore other ways to use its technology although for non-spam uses.